The present invention relates to the recording, storage and reading of magnetic data, particularly rotatable magnetic recording media, such as thin film magnetic disks having textured surfaces and a lubricant topcoat for contact with cooperating magnetic transducer heads.
Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. In operation, a typical contact start/stop (CSS) method commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk, where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk, and stopping.
For optimum consistency and predictability, it is necessary to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. Accordingly, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to excessive stiction and friction during the start up and stopping phases, thereby causing wear to the head and recording surfaces, eventually leading to what is referred to as a xe2x80x9chead crash.xe2x80x9d Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
Conventional practices for addressing these apparent competing objectives involve providing a magnetic disk with a roughened recording surface to reduce the head/disk friction by techniques generally referred to as xe2x80x9ctexturing.xe2x80x9d Conventional texturing techniques involve mechanical polishing or laser texturing the surface of a disk substrate to provide a texture thereon prior to subsequent deposition of layers, such as an underlayer, a magnetic layer, a protective overcoat, and a lubricant topcoat, wherein the texture on the surface of the substrate is intended to be substantially replicated in the subsequently deposited layers.
A typical longitudinal recording medium is depicted in FIG. 1 and comprises a non-magnetic substrate 10, typically an aluminum (Al)-alloy, such as an aluminum-magnesium (Alxe2x80x94Mg)-alloy, plated with a layer of amorphous nickel-phosphorus (NiP). Alternative substrates include glass, glass-ceramic materials, and graphite. Substrate 10 typically includes, sequentially deposited on each side thereof, a chromium (Cr) or a Cr-based alloy underlayer 11, 11xe2x80x2, a cobalt (Co)-based alloy magnetic layer 12, 12xe2x80x2, a protective overcoat 13, 13xe2x80x2, typically containing carbon (C), and a lubricant topcoat 14, 14xe2x80x2. Cr underlayer 11, 11xe2x80x2 can be applied as a composite comprising a plurality of sub-underlayers 11A, 11Axe2x80x2. Cr underlayer 11, 11xe2x80x2, Co-based alloy magnetic layer 12, 12xe2x80x2 and protective overcoat 13, 13xe2x80x2, typically containing carbon, are usually deposited by sputtering techniques performed in an apparatus containing sequential deposition chambers. A conventional Al-alloy substrate is provided with a NiP plating, primarily to increase the hardness of the Al substrate, serving as a suitable surface to provide a texture, which is substantially reproduced on the disk surface.
In accordance with conventional practices, a lubricant topcoat is uniformly applied over the protective layer to prevent wear between the disk and head interface during drive operation. Excessive wear of the protective overcoat, typically comprising carbon, increases friction between the head and disk, thereby causing catastrophic drive failure. Excess lubricant at the head-disk interface causes high stiction between the head and disk. If stiction is excessive, the drive cannot start and catastrophic failure occurs. Accordingly, the lubricant thickness must be optimized for stiction and friction.
Liquid lubrication of the disk surface has at least two problems which limit its effectiveness as used in rotating storage media. First, the lubricant does not have a retention means so that when the disk rotates, the lubricant spins off the disk. The depletion of the lubricant thickness from the disk surface increases the friction between the disk and the read/write head. Second, the depletion of the thickness of the lubricant is not uniform across the surface of the disk. Where the thickness is too thin, the head can cause wear on the disk surface. Where the lubricant thickness is too great, the head will become stuck in the lubricant (from static friction) and the head or disk could be damaged when the head suddenly becomes unstuck due to the rotating disk. Other failure modes include the inability of the spindle motor to start at all due to the static friction and failure of the mechanical suspension assembly. These effects are present even though the depletion is radial in nature.
A significant factor in the performance of a lubricant topcoat is the amount of lubricant which tightly adheres to the magnetic medium, as by chemical bonding forces operating between functional groups of the lubricant molecule and the surface of the recording medium. Typical conventional lubricants, such as perfluoroalkylpolyether (PFPE) fluids such as Fomblin Z-DOL, Fomblin Tx., and Fomblin Z-Tetraol, etc., generally are comprised of molecules having 2-4 polar groups at either end of a linear molecule. The polar end-groups provide bonding of the lubricant molecules to the surface of the magnetic medium. However, polar end-functional groups are not necessarily chemically inert and consequently, such conventional lubricants may disadvantageously undergo chemical reactions prior to their application to the magnetic medium tending to decrease their bonding potential. Moreover, the conventional perfluoroalkylpolyether-based lubricants do not have an optimal molecular structure or conformation considered necessary for the increased demands of magnetic medium lubricity.
One way in which to increase bonding of the lubricant to the disk surface and therefore prevent the depletion of lubricant therefrom has been to thermally bond the lubricant to the disk surface. However, this technique disadvantageously increases the exposure of the magnetic media to corrosion and degrades the reliability of the disk. Another technique is to use a process employing exposure to high energy electron beams. The lubricant is exposed to electron beams having an energy above ten KeV. This process has been shown to produce a modified lubricant film bonded to the disk surface. However, the modified film does not contain all the required lubricating properties of the unmodified film.
Thus, a significant factor in the performance of recording media is the quality and character of the topcoat lubricant. Lubricant topcoats comprised of conventional polymeric materials as described above are typically applied as a heterogeneous mixture of different molecular weight species. The use of such mixtures, however, results in dispersal or variation of the properties thereof, depending upon the relative amounts of each molecular weight fraction present in the mixture. As a consequence, use of polymer mixtures incurs difficulties in maintaining uniform processing conditions and product quality.
It is also desirable for improved media performance to employ lubricants which form an effective functional topcoat at a thickness less than those of conventionally utilized lubricants. As indicated above, perfluoropolyether lubricants with one or more functionalized end-groups are conventionally employed for recording media topcoats. The functionalized end-groups of these compounds are considered necessary to provide direct bonding, and thus, improved adhesion of the lubricant topcoat to the recording media. It is also believed, however, that for functionalized perfluoropolyether lubricants to provide the requisite tribology, they must be applied at a relatively high topcoat thickness, particularly when the recording medium is expected to perform under high stress conditions.
Perfluoropolyether lubricants with nonfunctionalized end-groups are also known. However, such lubricants have not found significant use as disk lubricants since they typically suffer from poor wear resistance. Moreover, commercially available terminally nonfunctional perfluoropolyether lubricants typically have wide and varying distributions of molecular weight components.
In view of the criticality of the lubricant topcoat, there is a continuing need for improved bonding of the lubricant to the magnetic recording medium, particularly to a carbon-based protective overcoat. There also exists a need for a lubricant topcoat providing improved stiction and wear performance, particularly under conditions of high stress, temperature, and humidity. There is also a need for lubricants which form functionally effective topcoats on recording media at a thickness less than conventional lubricant topcoats.
An advantage of the present invention are improved lubricants suitable for use as topcoats for magnetic recording media, wherein the lubricants comprise amphiphilic molecules having a central polyfunctional polar group moiety and a pair of fluoroalkyl ether end groups at respective ends of the central moiety.
Another advantage of the present invention is a magnetic recording medium comprising a lubricant topcoat thereon exhibiting good stiction and wear resistance, wherein the lubricant topcoat comprises an amphiphilic lubricant molecule.
Yet another advantage of the present invention is a method of manufacturing a magnetic recording medium having a lubricant topcoat comprising an amphiphilic lubricant molecule.
A still further advantage of the present invention is a method of making a symmetrically configured, amphiphilic lubricant.
Additional advantages and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the invention. The objects and advantages of the invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a substrate having a surface; and a lubricant topcoat on said substrate surface, wherein the lubricant topcoat comprises an amphiphilic lubricant molecule having a hydrophilic central portion including a plurality of polar functional groups and a pair of hydrophobic fluoroalkylether or perfluoroalkylether end portions at respective ends of the hydrophilic central portion.
According to embodiments of the present invention, the hydrophilic central portion of the lubricant molecule comprises an ester or amide; the lubricant has a molecular weight distribution of about 1.0; comprises a single molecular weight species; and the lubricant molecule has the formula: 
wherein:
A is alkyl, haloalkyl, alkoxy, haloalkoxy, aryl, or haloaryl;
R1 and R2 are independently C1-10 fluoroalkyl, or C1-10 perfluoroalkyl;
Z and Zxe2x80x2 are independently nitrogen, or oxygen;
x and y are between about 1 to about 10; and
R3 is alkylene, arylene, halosubstituted alkylene or arylene, or (Rxe2x80x94J)mxe2x80x94Rxe2x80x2; wherein R and Rxe2x80x2 are independently alkylene or arylene, or halosubstituted alkylene or arylene, J is NH, O, S, Sxe2x80x94S, SO2, C(O), or C(S) and m is 1-4.
According to particular embodiments of the present invention, the magnetic recording medium comprises: a substrate; an underlayer on the substrate; a magnetic layer on the underlayer; and the lubricant topcoat on the magnetic layer.
According to another aspect of the present invention, a method of manufacturing a magnetic recording medium comprises the sequential steps of:
(a) depositing a magnetic layer on a substrate;
(b) forming a protective overcoat layer over the magnetic layer; and
(c) depositing a lubricant layer on the protective overcoat layer to form a lubricant topcoat; wherein the lubricant topcoat comprises an amphiphilic lubricant molecule having a hydrophilic central portion including a plurality of polar functional groups and a pair of hydrophobic fluoroalkylether or perfluoroalkylether end portions at respective ends of the hydrophilic central portion.
According to embodiments of the present invention, step (c) comprises exposing the surface of the protective overcoat to a vapor comprising the lubricant or applying a solution of the lubricant in a solvent to the surface of the protective overcoat, the solvent being at least one selected from the group consisting of esters, ketones, alcohols, and fluorinated compounds.
According to particular embodiments of the present invention, the solvent is at least one selected from the group consisting of ethyl acetate, ethanol, and acetone; and the lubricant molecule has the formula: 
wherein:
A is alkyl, haloalkyl, alkoxy, haloalkoxy, aryl, or haloaryl;
R1 and R2 are independently C1-10 fluoroalkyl, or C1-10 perfluoroalkyl;
Z and Zxe2x80x2 are independently nitrogen or oxygen;
x and y are between about 1 to about 10; and
R3 is alkylene, arylene, halosubstituted alkylene or arylene, or (Rxe2x80x94J)mxe2x80x94Rxe2x80x2; wherein R and Rxe2x80x2 are independently alkylene or arylene, or halosubstituted alkylene or arylene, J is NH, O, S, Sxe2x80x94S, SO2, C(O), or C(S) and m is 1-4.
According to yet another aspect of the present invention, a method of producing a symmetrically configured amphiphilic lubricant compound having formula (I) 
comprises chemically combining two molecules of a compound of formula (II): 
with one molecule of a compound of formula (III)
xe2x80x83Hxe2x80x94Zxe2x80x94(R4)mxe2x80x94Zxe2x80x2xe2x80x94H
wherein:
A is alkyl, haloalkyl, alkoxy,. haloalkoxy, aryl, or haloaryl;
R1 and R2 are independently C1-10 fluoroalkyl, or C1-10 perfluoroalkyl;
Zxe2x80x2 and Z are independently nitrogen, or oxygen;
x and y are between about 1 to about 10;
m is 1 to 4; and
R4 is alkylene, alkylene-oxy, alkylene-thio, alkylene-dithio, alkylene-sulfonyl, or halosubstitued derivatives thereof.
According to particular embodiments of the present invention, the method comprises producing a compound of formula: 
Additional advantages of the present invention will become readily apparent to those having ordinary skill in the art from the following detailed description, wherein the embodiments of the invention are described, simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.